Air and Gas Injection in the Oil Fields of Illinois Page: 9
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RT. 3783
It is split into two or three persistent lenses that show average
depths- of about 850, 900 and 940 feet with an average interval between
the,,tops of the sands of about 50 feet. The thickness of the sand
lenses varies between 2 and 50 feet with an average of about 25 feet,
The wells in which one or two lenses are absent are too numerous to
mention. There are additional lenses of sand both above and below
the zone which includes the three persistent lenses, One above is
known. as the "gas" or "stray" sand. It is usually from 6 to 20 feet
thick and about 20 to 50 feet above the top-most lens of the Robinson
sand, The sand lens lower than the oil zone may belong to the
Robinson sand as a fourth lens, so closely is it related to the upper
lenses. There are other minor streaks of sand even in the producing
zone that add further confusion to the correlation,
Source.of Gas for Injection
The supply of natural gas in the old oil fields of Illinois usually
has been inadequate for gas injection. :[n the Colmar and Plymouth oil fields
of western Illinois, where the volume of natural gas produced is inadequate
to supply fuel for central-p6wer engines, air is injected into the oil sand.
Operators in the Robinson oil field in the southeastern part of the State
have been more fortunate. After air has been injected into the reservoir
for several months, enough gas is produced to provide fuel for engines on
most of the projects, and part of the produced air-gas mixture is reinjected.
Within the last 5 years, however, only air has been used as an injection
medium on several projects because the air-gas mixtures produced by the oil
wells have become deficient in gas.
Natural gas is produced in some of the newer oil fields in quantities
exceeding their requirements for gas injection and fuel. It is unfortunate
that gas from these fields (all of which are less than 70 miles from the
Robinson oil field) has not been used to replenish the diminishing supply
of gas in the older oil fields in that part of the State;
Development Practices
Ordinarily most operators of gas-injection projects.in the stripper
fields of Illinois have converted old oil wells to injection wells and have
drilled no new wells. On a few, large, well-organized projects one or more
wells have been drilled to obtain information on the reservoir. Absence of
extensive drilling programs has resulted in a material saving in the cost
of developing many projects, but the scarcity of core samples from the oil-
producing sands has made it difficult to design systematic gas-injection
projects, Thus, projects have been developed slowly, usually by experimental
injection, and it is common practice for an oil well to be converted to an
injection well and reconverted to a producing well within 1 year.
With few exceptions, the 12 oil-producing companies operating gas-
injection projects in the old oil fields have utilized second-hand equip-
ment in the development of their projects In the southeastern oil fields
gas pumps and compressors, utilized in vacuum operations and the
259-9239
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Keithly, C. M. & Jennings, Thomas. Air and Gas Injection in the Oil Fields of Illinois, report, November 1944; [Washington D.C.]. (https://digital.library.unt.edu/ark:/67531/metadc38426/m1/13/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.